The present invention relates to a sliding stem seal, particularly for the stem of an internal combustion engine intake or exhaust valve.
Seals of the aforementioned type are employed for preventing the tappet lubricating oil from seeping along the valve stem into the engine, and comprise a first cylindrical portion fitted onto a cylindrical portion of a bush supporting the stem and fitted inside the cylinder head; and a second cylindrical portion inside which is formed an annular lip cooperating with the valve stem. The tappet lubricating oil also lubricates the contact surface between the valve stem and sealing lip for reducing friction between the same.
When the engine is left idle for some time, the lubricating oil seeps out of the cylinder head, thus resulting in the sealing lip drying up and sticking to the valve stem when the engine is started again, the disadvantages of which are obvious.